XR21B1411IL-0A-EB Datasheet, PDF (5/30 Pages) Exar Corporation – ENHANCED 1-CH FULL-SPEED USB UART

XR21B1411
REV. 1.2.0
ENHANCED 1-CH FULL-SPEED USB UART
1.0 FUNCTIONAL DESCRIPTIONS
1.1 USB interface
The USB interface of the B1411 is compliant with the USB 2.0 Full-Speed Specifications.
The B1411 uses the following set of parameters:
 1 Control Endpoint
■ Endpoint 0 as outlined in the USB specifications
 1 Configuration is supported
 2 interfaces for the UART channel
■ Single interrupt endpoint
■ Bulk-in and bulk-out endpoints
1.1.1 USB Vendor ID
Exar’s USB Vendor ID is 0x04E2. This is the default Vendor ID that is used for the B1411. This value can be
changed by programming the internal OTP via the USB link.
1.1.2 USB Product ID
The default USB Product ID for the B1411 is 0x1411. This value can be changed by programming the internal
OTP via the USB link. Note that Exar’s custom drivers for all Windows OS require that the Product ID be an
odd number for the B1411 device for proper identification of the device.
1.2 USB Device Driver
The B1411 device can be used with either a standard CDC-ACM driver or a custom driver. When the CDC-
ACM driver is used, the driver has no capability to read or write the B1411 device registers. Because of this,
the B1411 device is initialized to the settings in Table 1. With a custom driver, all GPIOs default in hardware to
inputs but these settings may be modified by the custom driver.
TABLE 1: B1411 REGISTER DEFAULTS WITH CDC-ACM DRIVER
REGISTER
VALUE
NOTES
FLOW_CONTROL
0x001
Hardware flow control
GPIO_MODE
0x001
RTS / CTS flow control
GPIO_DIRECTION
0x008
GPIO3/DTR# configured as an output
GPIO_INT_MASK
0x030 GPIO0/RI#, GPIO1/CD# and GPIO2/DSR# are interrupt sensitive, i.e.
can cause a USB interrupt to be generated
These default settings can be overridden by programming the OTP via the Address Value feature.
Although there is no ability to read / write registers when using the CDC-ACM driver, basic UART functions,
including setting baud rate, character format and sending line break is supported by the CDC driver. Refer to
the 4 CDC_ACM_IF USB Control Commands listed in Table 2.
If a custom driver is used, the CUSTOM_DRIVER_ACTIVE bit should be immediately set to ’1’ by the driver.
Once the CUSTOM_DRIVER_ACTIVE bit is set, the custom driver can use standard CDC-ACM commands
without configuring the device to the default register settings used with the CDC-ACM driver. Any changes to
the register settings for the GPIOs and flow control will specifically need to be configured by the driver.
1.3 UART
The UART can be configured via USB control transfers from the USB host. The UART transmitter and receiver
sections are described separately below.
5